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If your doctor has recommended a biologic for Crohn's disease, you likely have a lot of questions: What is a biologic? Which biologics are used for Crohn's? Should I take one? If so, when -- and which one?

WebMD answers these commonly asked questions about biologics and suggests some other questions to ask your doctor -- and yourself -- to help you choose the treatment that's right for you.

What Are Biologics?

Also known as biologic response modifiers or biologic agents, biologics are geneticallyengineered therapies made from living organisms. Unlike some other Crohn's medications, which suppress the entire immune system, the biologic agents target specific players in the inflammatory response. For that reason, they may avoid some of the broad side effects that come with some other drugs.

Biologics have been used for a little over a decade. Remicade (infliximab) was the first biologic approved to treat Crohn's, in 1998. Today, there are four biologics approved for Crohn's treatment.

Cimzia (certolizumab), Humira (adalimumab), and Remicade work by inhibiting a protein called tumor necrosis factor alpha that's involved in inflammation. Another medication, Tysabri (natalizumab), blocks certain types of white blood cells that are involved in inflammation.

Should I Take a Biologic? If So, When?

Whether or not you take a biologic will depend largely on how severe your Crohn's is, which other treatments you have tried, your doctor's treatment philosophy, and your preference.

Biologics are FDA approved for people with moderate to severe active disease who have not had an adequate response to traditional treatments.

Some doctors, including Marie Borum, MD, professor of medicine and director of the Division of Gastroenterology and Liver Diseases at George Washington University in Washington, D.C., use what is called step-up therapy. A doctor who uses this approach does not suggest a biologic until you have tried and failed conventional treatments such as aminosalicylates, antibiotics, or drugs that suppress the immune system such as methotrexate, says Borum.

There are several reasons for the step-up approach, she says. "[Non-biologic] therapies have been around long, so we are more familiar with them -- we know how they work, we know what to expect and, because of our comfort level with them, we tend use them first and hold the biologics," says Borum.

Also, she says if you use a biologic early on, you exhaust your treatment options up front. "After that, if you have an exacerbation you may well be in a situation where you no longer have options," Borum says.

Others doctors, including Richard Bloomfeld, MD, are more likely to prescribe biologics from the start in hopes that they can help people avoid complications and surgery.

"Although there are other drugs I often use, anti-TNF biologics should not be reserved as a last-ditch effort," says Bloomfeld, associate professor of medicine and director of the Inflammatory Bowel Disease Program at Wake Forest University School of Medicine in Winston Salem, N.C. "The trend is to use biologics early in the disease course with the hope of altering the history of disease."

Most doctors agree that biologics should be started sooner rather thanlater for people with severe disease or with factors that indicate Crohn's likely will be severe.

"I think the challenge in Crohn's disease today is to identify people who are going to have an aggressive disease course in the future and would benefit from biologic therapy now," says Bloomfeld.

Factors doctors may consider when predicting whether Crohn's is severe enough to need a biologic -- or might become severe -- include:

Age at diagnosis. People who are diagnosed with Crohn's when they are young tend to have more severe disease.

Involvement of the small intestine. About 70% of Crohn's cases involve both the small and large intestine or small intestine only.

Need for corticosteroids. If you often need corticosteroids to control inflammation, you may be a candidate for a biologic therapy.

Smoking. Smokers generally have more severe disease than nonsmokers.

Fistulzing disease. Biologics may help heal fistulas, whichhappen when ulcers tunnel through two organs or parts of the body, such as two parts of the intestine.

Which Biologic Is Right for You?

When deciding on a biologic for Crohn's, doctors usually start with one of the TNF-inhibitors, says Bloomfeld. Tysabri is usually reserved for people who have failed anti-TNF therapy.

The TNF inhibitors have never been compared head-to-head in a study, so the decision to choose one over the other is largely about which one you and your doctor prefer.

How often you take the medication and how it's given may be factors in your decision. For example, two of the anti-TNF drugs, Humira and Cimzia, are given by injection -- Humira every two weeks; Cimzia every four weeks. Remicade is usually given every two months in two- to three-hour infusions at a doctor's office or infusion center.

Some people enjoy the convenience of the shot, says Prabhakar Swaroop, MD, assistant professor and director of the Inflammatory Bowel Disease Program at the University of Texas Southwestern Medical Center. "You can carry it with you and give it to yourself," he says. Others don't want to give themselves shots or just prefer to have an infusion administered in a medical setting.

Questions to Ask Your Doctor

Like all drugs, biologics have risks, and once you begin one, you will likely be on it for a long time. To determine if a biologic -- and if so, which one -- is right for you, ask your doctor the following questions:

How is the drug administered? Will I need to go for infusions or can I give it to myself?

Will this be the only treatment I need, or will I still have to take another drug along with it?

How often will I need to have infusions or shots?

Where would the infusion be given?

Are there any adverse reactions that might occur with shots or during infusions? If so, how are they treated?

What is the risk of side effects from the biologic? How does that compare with the risks of other treatments?

What benefits should I expect? How do those compare with the other options?

Is there a particular biologic that you have had experience or success with?

There are also questions you will need to ask yourself when choosing a biologic. A few questions to consider are:

Am I OK with giving myself shots? If not, is there someone who can give them to me if I have trouble?

Could I commit to giving myself shots consistently for a long time?

Would it be hard for me to sit still for two or more hours for an infusion? Would it be possible for me to get away from work or family responsibilities for infusions?

Do I prefer the convenience of a shot or would I feel more comfortable receiving treatment in a center from a health professional?